Fix: Ignoring error UnknownTopicOrPartition in partitionWatcher

[arxon31]

Second suggestion to fix issue #1314 with no rebalance after consumer in consumer group receives empty assignment

#1314

Cause of the issue:

1. Topic is not created
2. assignPartitions not fail with error
3. Topic created
4. partitionWatcher receives count of partitions from topic and fall through in loop
5. Group never rebalances

Solution:
partitionWatcher should ignore UnknownTopicOrPartition error and fall to loop with 0 start partitions count